US7675288B2 - Tunable magnetic field amplifying device - Google Patents

Tunable magnetic field amplifying device Download PDF

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Publication number
US7675288B2
US7675288B2 US12/182,359 US18235908A US7675288B2 US 7675288 B2 US7675288 B2 US 7675288B2 US 18235908 A US18235908 A US 18235908A US 7675288 B2 US7675288 B2 US 7675288B2
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Prior art keywords
magnetic field
tunable
sheet
amplifying device
swiss roll
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US12/182,359
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US20090153275A1 (en
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Wangjoo Lee
Dong-Ho Kim
Jae-Ick Choi
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Electronics and Telecommunications Research Institute ETRI
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Electronics and Telecommunications Research Institute ETRI
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J3/00—Continuous tuning
    • H03J3/20—Continuous tuning of single resonant circuit by varying inductance only or capacitance only

Definitions

  • the present invention relates to a tunable magnetic filed amplifying device; and, more particularly, to a magnetic field amplifying device capable of easily adjusting resonance frequencies and varying usable bands by using discrete elements to vary electric properties of elements used for amplifying a magnetic field of a specific microwave band.
  • Magnetic Resonance Imaging widely used in the diagnosis of disease is a high-tech non-destructive, non-radioactivity inspection method that is excellent in efficacy but causes no load to the human body.
  • the MRI inspection method applies a static magnetic field of about 0.5 Tesla or greater to a target region of a body. Then, protons in the body have a resonance frequency proportional to the strength of a static magnetic field at about several tens of MHz band or higher.
  • an electromagnetic wave of such resonance frequency is irradiated in the shape of a pulse to the body, protons absorb the energy of the wave and become excited. After a certain period of time, the protons emit electromagnetic waves of the same frequency and lose energy, thereby going down to a low energy state.
  • the wave being generated at this time is called a Magnetic Resonance (MR) signal.
  • the MRI inspection method receives this MR signal through a receiving antenna and creates 2-D images representing the density distribution of protons.
  • contrast media or contrast agents for MRI are widely used to improve the resolution for X-ray inspection.
  • MRI contrast media are also actively researched now because they can increase the resolution without placing so much cost burden on the patients.
  • the MRI contrast media are used in a drug delivery way, so they may cause inconvenience to patients and it may take some time until they are actually used.
  • the MR signal is essentially an electromagnetic wave of a specific frequency, and composed of two vector components, an electric field vector and a magnetic field vector. But, unlike typical waves traveling in air or vacuum space environment, the MR signal is characterized that the magnetic field strength has a predominant role over the electric field strength. Therefore, a kind of electrical resonant circuit called Swiss roll, which is very sensitive to a change in magnetic field at a specific frequency, is arranged between the body and a receiving antenna in order that a loss in the MR signal can be reduced.
  • Swiss roll which is very sensitive to a change in magnetic field at a specific frequency
  • the Swiss roll which is a magnetic field amplifying device, consists of a central mandrel upon which a spiral metal sheet coated with dielectric is wound in the shape of a cylinder N times, so that when an external magnetic field corresponding to its resonance frequency is inputted, it causes an electromagnetic resonance to amplify the magnetic field strength.
  • an object of the present invention to provide a magnetic field amplifying device capable of easily adjusting resonance frequencies and tuning usable bands by using discrete elements to vary electric properties of elements that are used for amplifying a magnetic field of a specific microwave band.
  • a tunable magnetic field amplifying device including: a Swiss roll formed by winding a metal sheet coated with a dielectric in a spiral cylinder shape once or several times; and a tunable capacitor connected between an inner sheet of and an outer sheet of the metal sheet for tuning a resonance.
  • the tunable magnetic field amplifying device may further include a tunable inductor connected serially to the tunable capacitor for increasing a tunable range of the resonance frequency.
  • a tunable magnetic field amplifying device including: a Swiss roll formed by winding a metal sheet coated with a dielectric in a spiral cylinder shape once or several times; and a tunable inductor connected between an inner sheet and an outer sheet of the metal sheet for tuning a resonance frequency.
  • FIG. 1 is a view for explaining an induced current and an induced magnetic field according to a magnetic field change.
  • FIG. 2A and FIG. 2B are views for explaining a magnetic field amplifying device with a conventional Swiss roll structure.
  • FIG. 3A is an equivalent circuit of FIG. 1 .
  • FIG. 3B is an equivalent circuit of a conventional Swiss roll.
  • FIG. 4A illustrates the structure of a magnetic field amplifying device in accordance with one embodiment of the present invention.
  • FIG. 4B is an equivalent circuit of FIG. 4A .
  • FIG. 5A illustrates the structure of a magnetic field amplifying device in accordance with another embodiment of the present invention.
  • FIG. 5B is an equivalent circuit of FIG. 5A .
  • a structure 101 upon which a thin metal foil with a radius r is wound in the shape of a cylinder as shown in FIG. 1 will be explained first, before explaining the present invention.
  • an external magnetic field is Ho
  • the size per unit length of induced current flowing in the circumference direction of the cylinder is j.
  • the strength of the induced magnetic field inside the cylinder becomes j.
  • the induced magnetic field becomes a little smaller than j. Because of this, it is assumed that the strength of the induced magnetic field is ⁇ j (where ⁇ satisfies the inequality of 0.5 ⁇ 1 for convenience).
  • the demagnetizing field means that, when a magnet such as a bar magnet is magnetized by applying an external magnetic field, a magnetic field is created inside the bar magnet in opposite direction to the external magnetic field due to stimuli caused at both ends of the bar magnet.
  • both the induced current and the induced magnetic field become time dependent in the same form of e ⁇ iwt .
  • EMF Electromotive Force
  • ⁇ denotes a magnetic flux
  • B indicates a magnetic flux density
  • ⁇ is a resistance per unit length in the circumference direction of a cylinder.
  • FIGS. 2A and 2B show slightly modified shapes of the cylinder depicted in FIG. 1 , in which a thin rectangular metal conductive sheet is wound overlappingly at the end. This corresponds to an electromagnetic device 201 called a Swiss roll for amplifying a magnetic field.
  • the simple cylinder shown in FIG. 1 becomes a circuit where an inductance L and a resistor R are connected in series to a voltage source as shown in FIG. 3A
  • the Swiss roll shown in FIGS. 2A and 2B becomes a serial resonance circuit, which has a capacitance component in addition to the inductance and the resistor connected to a voltage source, as shown in FIG. 3B .
  • the cylinder shape Swiss roll having a capacitance component added thereto has the function of amplifying an external magnetic field of a specific frequency.
  • the problem with using the Swiss roll is that the frequency of an external magnetic field is mostly determined in advance.
  • ‘r’ and ‘C’ in Eq. (9) should be finely adjusted in order to match the resonance frequency of the Swiss roll with the frequency of an external magnetic field.
  • the present invention employed discrete capacitors and inductors whose capacitance and inductance can be adjusted, such that the resonance frequency of the Swiss roll can be adjusted easily and a usable band can be varied, thereby making it possible to use a single Swiss roll under various external magnetic field conditions of different frequencies.
  • FIG. 4A illustrates the structure of a Swiss roll, which is a magnetic field amplifying device, in which discrete tunable capacitors 402 are connected between an inner metal sheet and an outer metal sheet.
  • FIG. 4B shows an equivalent circuit of FIG. 4A .
  • the magnetic field amplifying device in accordance with the present invention is further provided with tunable capacitors 402 connected between the inner and the outer metal sheet in the general Swiss roll.
  • the tunable magnetic field amplifying device of the present invention further has a tunable capacitor 406 - 1 connected parallely to the parasitic capacitor 406 , in the general Swiss roll structure which is consisted of an inductor (L) 404 , a resistor (R) 405 , and a parasitic capacitor (C) 406 . Therefore, by adjusting the capacitance of the tunable capacitor 406 - 1 , the invention magnetic field amplifying device can easily change the resonance frequency of a Swiss roll.
  • the innermost metal sheet and the outermost metal sheet may be connected via a through hole 403 .
  • a voltage controlled varactor or a mechanically adjusted capacitor may be used as the tunable capacitor.
  • the magnetic field amplifying device in accordance with the present invention may employ a tunable inductor to change the resonance frequency.
  • the magnetic field amplifying device of the present invention has a tunable inductor connected between the inner and the outer metal sheet, in the structure of the existing Swiss roll.
  • the present invention can use the tunable inductor to vary the resonance frequency of the Swiss roll.
  • FIG. 5A illustrates a magnetic field amplifying device in accordance with another embodiment of the present invention
  • FIG. 5B is an equivalent circuit of FIG. 5A .
  • the magnetic field amplifying device of this embodiment is characterized by connecting a tunable inductor serially to a tunable capacitor. If a parasitic capacitance at an overlapped portion of a metal sheet is very small, an equivalent circuit of FIG. 5A reduces to FIG. 5B .
  • the magnetic field amplifying device in accordance with another embodiment of the present invention has a structure that a tunable capacitor 502 and a tunable inductor 503 are serially connected between the inner sheet and the outer sheet of a metal sheet, in the structure of a conventional Swiss roll.
  • the magnetic field amplifying device of this embodiment is configured in a manner that a structure that a tunable inductor 504 - 1 and a tunable capacitor 506 - 1 are serially connected to each other, in the structure of a conventional Swiss roll consisting of an inductor (L) 504 , a resistor (R) 505 , and a parasitic capacitor (this is omitted in FIG. 5B if it is very small). Therefore, by adjusting the tunable capacitor and the tunable inductor, the magnetic field amplifying device of this embodiment can further increase the tunable range of the resonance frequency of a Swiss roll.
  • the present invention can easily tune the resonance frequency of the Swiss roll to the frequency of an external magnetic field to be amplified and allows a Swiss roll to be used in a very wide range, by adding tunable capacitors and inductors consisting of discrete elements.
  • a Swiss roll can be broadly used in a magnetic field sensor, and particularly, when the Swiss roll can be used for the MRI, it can improve the resolution of MRI images without incurring extra charge.

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Engineering & Computer Science (AREA)
  • Medical Informatics (AREA)
  • Biophysics (AREA)
  • Pathology (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Biomedical Technology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Radiology & Medical Imaging (AREA)
  • Molecular Biology (AREA)
  • Surgery (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
US12/182,359 2007-12-12 2008-07-30 Tunable magnetic field amplifying device Expired - Fee Related US7675288B2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR10-2007-0129017 2007-12-12
KR1020070129017A KR20090061974A (ko) 2007-12-12 2007-12-12 동작 주파수가 가변되는 자기장 강화 장치

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090121716A1 (en) * 2007-11-13 2009-05-14 Bruker Biospin Gmbh NMR resonator configured as an insulated foil, conductively coated on both sides
US10948556B2 (en) 2017-11-30 2021-03-16 Electronics And Telecommunications Research Institute Method for modifying and controlling magnetic field and apparatus for the same

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EP2551988A3 (en) * 2011-07-28 2013-03-27 General Electric Company Dielectric materials for power transfer system
EP2551250B1 (en) * 2011-07-28 2016-12-07 General Electric Company Dielectric materials for power tranfer system
CN104352239B (zh) * 2014-11-18 2016-08-24 辛学刚 一种磁共振人体组织电特性断层成像方法
EP4134991A1 (en) 2016-08-10 2023-02-15 IUCF-HYU (Industry-University Cooperation Foundation Hanyang University) Magnetic tube system
US11391798B2 (en) * 2019-01-03 2022-07-19 Electronics And Telecommunications Research Institute Continuous scanning method using signal shielding and apparatus for the same

Citations (9)

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JPS62190708A (ja) 1986-02-18 1987-08-20 Mitsubishi Electric Corp 高周波磁場発生・検出器
US4973908A (en) * 1989-06-23 1990-11-27 General Electric Company NMR probe with multiple isolated coplanar surface coils
US5500552A (en) * 1993-07-26 1996-03-19 T.I.F. Co., Ltd. LC element, semiconductor device and LC element manufacturing method
US5959515A (en) * 1997-08-11 1999-09-28 Motorola, Inc. High Q integrated resonator structure
US6480110B2 (en) * 2000-12-01 2002-11-12 Microchip Technology Incorporated Inductively tunable antenna for a radio frequency identification tag
US6791432B2 (en) 2000-03-17 2004-09-14 The Regents Of The University Of California Left handed composite media
US7081753B2 (en) * 2004-07-26 2006-07-25 Varian, Inc. Multiple tuned scroll coil
US7385398B2 (en) * 2005-05-20 2008-06-10 Bruker Biospin Gmbh Radio frequency coil arrangement for magnetic resonance measurements and probe head for measuring resonance signals by utilizing such a radio frequency coil arrangement
US20090237178A1 (en) * 2008-03-20 2009-09-24 Industrial Technology Research Institute Circuit device having inductor and capacitor in parallel connection

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS62190708A (ja) 1986-02-18 1987-08-20 Mitsubishi Electric Corp 高周波磁場発生・検出器
US4973908A (en) * 1989-06-23 1990-11-27 General Electric Company NMR probe with multiple isolated coplanar surface coils
US5500552A (en) * 1993-07-26 1996-03-19 T.I.F. Co., Ltd. LC element, semiconductor device and LC element manufacturing method
US5959515A (en) * 1997-08-11 1999-09-28 Motorola, Inc. High Q integrated resonator structure
US6791432B2 (en) 2000-03-17 2004-09-14 The Regents Of The University Of California Left handed composite media
US6480110B2 (en) * 2000-12-01 2002-11-12 Microchip Technology Incorporated Inductively tunable antenna for a radio frequency identification tag
US7081753B2 (en) * 2004-07-26 2006-07-25 Varian, Inc. Multiple tuned scroll coil
US7385398B2 (en) * 2005-05-20 2008-06-10 Bruker Biospin Gmbh Radio frequency coil arrangement for magnetic resonance measurements and probe head for measuring resonance signals by utilizing such a radio frequency coil arrangement
US20090237178A1 (en) * 2008-03-20 2009-09-24 Industrial Technology Research Institute Circuit device having inductor and capacitor in parallel connection

Non-Patent Citations (2)

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Title
Pendry et al.; Magnetism from Conductors and Enhanced Nonlinear Phenomena; IEEE Transactions on Microwave Theory and Techniques, vol. 47, No. 11, Nov. 1999; pp. 2075-2084.
Wiltshire et al.; Microstructured Magnetic Materials for RF Flux Guides in Magnetic Resonance Imaging; Science, vol. 291, Feb. 2, 2001; pp. 849-851.

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090121716A1 (en) * 2007-11-13 2009-05-14 Bruker Biospin Gmbh NMR resonator configured as an insulated foil, conductively coated on both sides
US7795871B2 (en) * 2007-11-13 2010-09-14 Bruker Biospin Gmbh NMR resonator configured as an insulated foil, conductively coated on both sides
US10948556B2 (en) 2017-11-30 2021-03-16 Electronics And Telecommunications Research Institute Method for modifying and controlling magnetic field and apparatus for the same

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US20090153275A1 (en) 2009-06-18

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